1. Technical Field of the Invention
The present invention concerns a magnetic thin film and a magnetic thin film manufacturing method. The magnetic thin film of the present invention can be used as a magnetic shield or a magnetic body in a thin-film magnetic head which is suitable for high-density magnetic recording; this magnetic thin film has a high saturation flux density, is superior in terms of soft magnetic characteristics, and has a high resistivity.
Furthermore, the present invention also concerns a thin-film magnetic head manufacturing method.
2. Background Information
In recent years, thin films formed by plating have been widely used in electronic parts, etc., not only for decorative purposes and anti-corrosion purposes, but also as functional thin films with specified functions. For example, permalloy magnetic thin films manufactured by plating processes are used as magnetic bodies in thin-film magnetic heads of hard disk drives, which are external memory devices used in computers. Permalloy is a typical soft magnetic thin film material; in particular, a permalloy alloy consisting of 82 atomic % Ni and 18 atomic % Fe is characterized by a magnetostriction constant of zero or a magnetostriction constant which has a negative value.
Over the years, there have been increasingly stronger demands for increased capacity and reduced size in hard disk drives; accordingly, recording densities have become increasingly higher, and materials with higher saturation flux densities have been required in the magnetic bodies of heads used to read such high-density recording. In order to obtain a higher saturation flux density in a permalloy magnetic thin film, it is necessary to increase the Fe content; however, if the Fe content is excessively increased, the magnetostriction constant increases so that the playback performance becomes unstable. Accordingly, there are limits to how far the saturation flux density can be increased in a simple permalloy magnetic thin film.
Meanwhile, Co-Ni-Fe ternary alloys have attracted attention as magnetic materials which can be used in place of permalloy materials with a composition of 82 atomic % Ni and 18 atomic % Fe.
FIG. 4 is an explanatory diagram which shows the relationship between composition and distribution of saturation flux density in Co-Ni-Fe ternary alloys. The composition region indicated by A in this figure shows a high saturation flux density and a small magnetostriction constant. Accordingly, alloys with compositions in this region may be expected to show promise as magnetic materials for thin-film magnetic heads. A magnetic thin film with a magnetostriction constant of zero and a high saturation flux density is described in U.S. Pat. No. 4,661,216.
However, the effective resistivity of the aforementioned Co-Ni-Fe ternary alloys in the composition region indicated by A in FIG. 4 is low, i. e., approximately 10 mW.diamond. cm. As a result, thin-film magnetic heads using Co-Ni-Fe ternary alloys suffer from the following new problems: i. e., both the writing characteristics and the reading characteristics are unstable in the high-frequency region, and the high-frequency response characteristics are inferior.
This point may be described in detail as follows:
Specifically, when a thin-film magnetic head is exposed to a change in magnetization, an eddy current is generated inside the magnetic material. Furthermore, as the magnetization response frequency of the thin-film magnetic head increases, i. e., as the change in the magnetization of the thin-film magnetic head per unit time increases, the eddy current flowing through the interior of the magnetic material increases.
Meanwhile, this eddy current generates a magnetic flux which hinders the change in magnetic flux sic! according to Lenz's law. As a result, the change in magnetization is suppressed as the frequency of the signal increases. Here, the eddy current flowing through the magnetic material is inversely proportional to the resistivity of the magnetic material.
Furthermore, as was described above, the value of the effective resistivity is low in the abovementioned composition region of Co-Ni-Fe ternary alloys, so that both the writing characteristics and reading characteristics are unstable in the high-frequency region. Accordingly, in cases where thin-film magnetic heads are manufactured using such alloys, the high-frequency response characteristics are inferior.
Good high-frequency response characteristics are indispensable in the magnetic materials of thin-film magnetic heads used in high-density recording. Accordingly, raising the resistivity of Co-Ni-Fe ternary alloys has been a technical problem requiring solution in order to allow the use of such alloys in thin-film magnetic heads.
Furthermore, high-resistivity magnetic thin films which have superior high-frequency response characteristics include magnetic thin films which have a hetero-amorphous two-phase structure (Japanese Patent Application Kokai No. 61-264698), and laminated magnetic thin films in which a nonmagnetic layer is laminated with a magnetic layer which has a hetero-amorphous two-phase structure (Japanese Patent Application Kokai No. 1-175707). However, since these films have an amorphous structure, film formation by means of a plating process is practically impossible, and such films must therefore be formed using a dry process such as sputtering, etc. However, since dry processes require a high degree of vacuum, such processes have a poor production efficiency compared to plating processes. Furthermore, because of the burning of resists (indispensable for the formation of fine elements) due to the rise in temperature that occurs during dry processes, milling processes must be used, so that the manufacturing process becomes complicated. Thus, magnetic thin films which have a hetero-amorphous two-phase structure and laminated magnetic thin films in which a nonmagnetic layer is laminated with a magnetic layer which has a hetero-amorphous two-phase structure suffer from drawbacks in terms of production efficiency, and are difficult to use industrially.
Accordingly, a magnetic thin film which allows the utilization of a plating process with superior productivity, and which has a high resistivity and a high saturation flux density, has not yet been developed, nor has any method for manufacturing such a film been developed.
Thus, in view of the abovementioned problems encountered in the prior art, the object of the present invention is to establish a method in which an electroplating process is utilized in order to manufacture soft magnetic thin films which have a high resistivity and a high saturation flux density, and to develop a method for manufacturing thin film magnetic heads utilizing the abovementioned method for manufacturing magnetic thin films.
Specifically, the object of the present invention is to provide a! a magnetic thin film i! which is used mainly as a magnetic material in thin-film magnetic heads suitable for high-density magnetic recording, ii! which is manufactured by means of a plating process, and iii! which has a high saturation flux density, superior soft magnetic characteristics and a high resistivity, and b! a method for manufacturing such magnetic thin films.